fs/notify: call exportfs_encode_fid with s_umount

{
  "id": "d7ac0ab0f0b38909f6d4436e286d0944be416e5fa58553d83d8ac453cc17ee2b",
  "url": "https://osv.dev/vulnerability/CVE-2025-40237",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "fs/notify: call exportfs_encode_fid with s_umount",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: fs/notify: call exportfs_encode_fid with s_umount Calling intotify_show_fdinfo() on fd watching an overlayfs inode, while the overlayfs is being unmounted, can lead to dereferencing NULL ptr. This issue was found by syzkaller. Race Condition Diagram: Thread 1 Thread 2 -------- -------- generic_shutdown_super() shrink_dcache_for_umount sb->s_root = NULL | | vfs_read() | inotify_fdinfo() | * inode get from mark * | show_mark_fhandle(m, inode) | exportfs_encode_fid(inode, ..) | ovl_encode_fh(inode, ..) | ovl_check_encode_origin(inode) | * deref i_sb->s_root * | | v fsnotify_sb_delete(sb) Which then leads to: [ 32.133461] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000006: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI [ 32.134438] KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037] [ 32.135032] CPU: 1 UID: 0 PID: 4468 Comm: systemd-coredum Not tainted 6.17.0-rc6 #22 PREEMPT(none) [ 32.143353] Call Trace: [ 32.143732] ovl_encode_fh+0xd5/0x170 [ 32.144031] exportfs_encode_inode_fh+0x12f/0x300 [ 32.144425] show_mark_fhandle+0xbe/0x1f0 [ 32.145805] inotify_fdinfo+0x226/0x2d0 [ 32.146442] inotify_show_fdinfo+0x1c5/0x350 [ 32.147168] seq_show+0x530/0x6f0 [ 32.147449] seq_read_iter+0x503/0x12a0 [ 32.148419] seq_read+0x31f/0x410 [ 32.150714] vfs_read+0x1f0/0x9e0 [ 32.152297] ksys_read+0x125/0x240 IOW ovl_check_encode_origin derefs inode->i_sb->s_root, after it was set to ",
    "evidence": "osv:CVE-2025-40237",
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      "modified": "2026-10-28T02:30:51.361959080Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/3f307a9f7a7a2822e38ac451b73e2244e7279496",
        "https://git.kernel.org/stable/c/950b604384fd75d62e860bec7135b2b62eb4d508",
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  "source_id": "core-osv",
  "document_id": 520044,
  "published_at": "2025-12-04T15:31:27.325+00:00"
}